This invention relates generally to an electrophotographic printing machine, and more particularly concerns an improved development system for use therein.
In electrophotographic printing, the photoconductive member is charged to sensitize the surface thereof. The charged photoconductive member is exposed to a light image of the original document being reproduced. Exposure of the sensitized photoconductive surface discharges the charge selectively. This records an electrostatic latent image on the photoconductive surface corresponding to the informational areas contained within the original document being reproduced. Development of the electrostatic latent image recorded on the photoconductive surface is achieved by bringing developer material into contact therewith. The developer material generally comprises dyed or colored heat-settable plastic powders, known in the art as toner particles, which are mixed with coarser carrier granules, such as ferromagnetic granules. The toner particles and carrier granules are selected such that the toner particles acquire the appropriate charge relative to the electrostatic latent image recorded on the photoconductive surface. Thus, when developer material is brought into contact with the latent image recorded on the photoconductive surface, the greater attractive force thereof causes the toner particles to transfer from the carrier granules and adhere to the electrostatic latent image. This concept was originally disclosed by Carlson in U.S. Pat. No. 2,297,691 and is further amplified and described by many related patents in the art.
Various methods have been developed for applying developer material to the latent image. For example, the developer material may be cascaded over the latent image with the toner particle being attracted from the carrier granules thereto. Other apparatus employed to develop latent image include magnetic field producing devices which form brush-like tufts extending outwardly therefrom contacting the photoconductive surface.
With the advent of single component developer materials, i.e. conductive magnetic particles, carrier granules are no longer required.
It is apparent that during the development cycle, toner particles are depleted from the developer mix, or the single component developer material, itself, is depleted. Thus, additional particles must be furnished to maintain copy density at a substantially optimum level. In order to produce an efficient printing machine, it is necessary to conveniently and effectively replace the particles used in the formation of copies.
Hereinbefore, toner particles have been dispensed from a trough or hopper into the developer mix. However, more frequently the toner particles within the hopper bridge or cake so as to prevent the free flow thereof from the hopper to the developer material contained within the sump of the development system. This frequently results in light copies and customer dissatisfaction. In the past, this condition has been corrected by periodically manually stirring the toner particles contained within the replenishment container.
Accordingly, it is the primary object of the present invention to improve particle dispensing by preventing bridging and caking of the particles.